80% of all antibiotics used in the United States are fed to farm animals. Cows, pigs, chickens, turkeys and goats are pumped with antibiotics to promote growth and prevent infections they don't even have. Not only is this unhealthy for the animals, but whoever eats them and their products is consuming a load of antibiotics as well. This major health issue leads to antibiotic resistance.
[FDA Summary report on antimicrobials sold or distributed for use in food-producing animals. Department of Health and Human Services]